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    SubjectRe: [PATCH 3/5] tty: handle VT specific compat ioctls in vt driver
    On Fri, Aug 07, 2009 at 10:57:32AM +0100, Alan Cox wrote:
    > On Fri, 7 Aug 2009 08:23:58 +0200
    > Frederic Weisbecker <fweisbec@gmail.com> wrote:
    >
    > > Hi,
    > >
    > >
    > > On Thu, Aug 06, 2009 at 03:09:28PM +0200, Arnd Bergmann wrote:
    > > > The VT specific compat_ioctl handlers are the only ones
    > > > in common code that require the BKL. Moving them into
    > > > the vt driver lets us remove the BKL from the other handlers
    > > > and cleans up the code.
    > >
    > >
    > > Why does it require the bkl?
    >
    > It's always taken the BKL - you have to prove it doesn't need it. Which
    > btw isn't true - it does need it in various places still.
    >
    > Alan


    It was a way to tell "I would like to know what it is protecting" ;-)
    I can imagine it is not here for no reason, the problem is to find why.

    As an example, to find the reason of the following lines in do_tty_hangup():

    /* inuse_filps is protected by the single kernel lock */
    lock_kernel();

    I had to look at a 2.2 kernel. At this time, inuse_filps existed,
    and now it is replaced by the tty->tty_files field, which
    is protected by file_list_lock().

    So according to the comment, we can remove the bkl there, but what
    guarantees its role hasn't evolved since then to make it protecting
    something else...



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